title: 1,3-Dipolar cycloaddition of organic azides to alkynes by a dicopper-substituted silicotungstate.
abstract: The dicopper-substituted gamma-Keggin silicotungstate TBA 4[gamma-H2SiW10O36Cu2(mu-1,1-N3)2] (I, TBA = tetra- n-butylammonium) could act as an efficient precatalyst for the regioselective 1,3-dipolar cycloaddition of organic azides to alkynes. Various combinations of substrates (four azides and eight alkynes) were efficiently converted to the corresponding 1,2,3-triazole derivatives in excellent yields without any additives. The present system was applicable to a larger-scale cycloaddition of benzyl azide to phenylacetylene under solvent-free conditions (100 mmol scale) in which 21.5 g of the analytically pure corresponding triazole could be isolated. In this case, the turnover frequency and the turnover number reached up to 14,800 h(-1) and 91,500, respectively, and these values were the highest among those reported for the copper-mediated systems so far. In addition, I could be applied to the one-pot synthesis of 1-benzyl-4-phenyl-1H-1,2,3-triazole from benzyl chloride, sodium azide, and phenylacetylene. The catalyst effect, kinetic, mechanistic, and computational studies show that the reduced dicopper core plays an important role in the present 1,3-dipolar cycloaddition.
authors.affiliation: Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Keigo
authors.initials: K
authors.lastname: Kamata
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Nakagawa
authors.forename: Kazuya
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Noritaka
authors.initials: N
authors.lastname: Mizuno
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D001386:Azides / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry; D003500:Cyclization; D008958:Models, Molecular; D015394:Molecular Structure; D017640:Silicates / Q000737:chemistry*; D013053:Spectrophotometry; D017973:Tungsten Compounds / Q000737:chemistry*
chemical_list: D000480:Alkynes; D001386:Azides; D017640:Silicates; D017973:Tungsten Compounds; D003300:Copper; C021746:silicotungstic acid